Art and Science of Laboratory Medicine

Art and Science of Laboratory Medicine

Sunday, July 14, 2013

Is The Order of Draw Just A Myth?

 The potential for cross-contamination of additives among evacuated blood tubes has led to the development of the order of draw. This practice, however, is mainly based on scarce, anecdotal, and mostly outdated literature data. Therefore, the goal of this investigation was to definitely establish whether or not the indication of a specific order of draw is still justified.

No significant difference could be observed between the first and the second serum tubes for any of the parameters. The bias calculated with Bland-Altman plots did not achieve statistical significance when the serum tube was collected after either a K2-EDTA or a sodium citrate tube.

According to this data, revision of national and supranational recommendations on blood collection by venipuncture should consider that the order of draw exerts a negligible effect on sample quality, and this aspect should no longer be considered a quality criterion when evaluating the performance of phlebotomists. 

Read more:
The order of draw: myth or science?

Source: Unbound medline

Art and Science of Laboratory Medicine

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Unknown said...

The sample size of 115 is laughably small to suggest such sweeping changes, especially since we in the lab see the effects of EDTA cross-contamination all the time. Or do the authors have another explanation for the severe hyperkalemia/hypocalcemia we see when the order of draw is ignored, the effects of which "mysteriously" disappear after a re-draw?

I'd venture to guess that the people who set up the study have never actually worked in a lab.

Unknown said...

Did they collect the sample according to normal protocol? What if they tilt the tubes to purposely contaminate the needle on the vacutainer holder? Why didn't they test affects on coagulation results? Contamination with potassium may be negligible but may affect these results. Did the serum tubes have no additive OR clot activator in them? This would also affect coagulation results as well. I would want more studies to be performed before I change my SOPs AND what I am teaching nursing staff when they transfer blood.

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